Gas Trap Kalashnikov
By Frank Iannamico

Gas Trap. If you mention those two words to a collector of M1 Garand rifles you will immediately get their attention. If mentioned to an AK enthusiast, you will probably just get a puzzled look.

The gas trap system works by trapping gas pressure after it leaves the muzzle, and uses that pressure to operate the weapon’s action. This gas trap is different than most modern gas operated systems, which tap gas pressure from a port drilled into the barrel, ahead of the gas piston. One advantage of the gas trap system is that gas trapped at the muzzle has a lower pressure than gas directed through a port in the barrel. There have been a few well-known production rifles to use the gas trap system; the Bang rifle, the German Gewehr 41 and early production M1 Garand rifles. The use of the gas trap system in the U.S. M1 was short lived, replaced by a port system during 1939. Original, unaltered gas trap M1 rifles are very rare and command a high premium that die-hard Garand collectors seem more than willing to pay.

The Garand gas trap system had a gap between the muzzle end-cap and the barrel. As the bullet left the barrel, some of the high-pressure gas generated by the burning gunpowder passed through the gap into the gas cylinder, pushing the piston rearward, operating the weapon’s action. After the M1 was put into service, the disadvantages of the gas trap systems were revealed. Considered one of the primary problems was the carbon deposit forming at the end of the barrel, which would partially obstruct the gap that the gas passed through. If too much carbon built up, the action would become sluggish, and eventually the rifle would malfunction. Another problem arose when cleaning the rifle. Cleaning patches would get caught and sometimes be left in the gap, restricting gas flow to the action.

A new gas system was designed for the M1, which had a .0805 inch gas port drilled into the bottom of the barrel. The high-velocity gas moving through the small port was largely self-cleaning, and the muzzle cap of the gas trap system could be eliminated. The new system was recommended by the Ordnance Committee on 26 October 1939. M1 rifles with the new barrels and gas cylinder assemblies were placed in production during 1940 and most all of the older gas trap Garands were retrofitted with the new system.

Krebs Custom

There are a growing number of talented gunsmiths that focus their talents on the AK pattern rifles; a weapon that has in recent years, become very, very popular with enthusiasts interested in martial arms. Most of today’s AK builders are concentrating on duplicating semiautomatic clones of AKs from different countries around the world. Most are meticulous down to the smallest detail; right down to using the correct rivet design. Krebs Custom of Illinois is a different breed of AK builder. Instead of replicating, the crew at Krebs Custom primarily concentrates on innovating. Heading the team at Krebs Custom is Marc Krebs, an AK enthusiast and a nationally known gunsmith, garnering his initial fame from building high-quality 1911 pistols for IPSC, IDPA competitions as well as personal protection handguns. Krebs Custom has more recently become very well known and respected among AK enthusiasts for applying their gunsmith skills to build AK rifles. As an AK enthusiast, Marc Krebs realized that the most desired, albeit unobtainable, AK would be a Russian made example. With this in mind he decided to obtain Russian made Saiga sporter rifles, with genuine Izhmash factory made receivers, and convert them into a military configuration.

Krebs’ attention to detail and quality workmanship coupled with the Izhmash Arsenal AK rifles result in a Russian Kalashnikov rifle that is extraordinarily smooth, accurate, reliable and aesthetically pleasing. In the conversion from sporter to military configuration, Krebs Custom uses only high quality new parts. What original parts are not available Krebs manufactures in-house, insuring that all of the parts meet or exceed the quality of the original Russian components.

The Gas Trap AK

Standard AK gas systems function by tapping gas pressure from a port drilled in the top of the barrel. After a cartridge is fired the bullet travels down the barrel at a very high velocity, being pushed by gas pressure generated by rapidly burning gun powder. Once the bullet passes the port in the barrel, hot high pressure gas behind the bullet is siphoned up through the gas port and acts on the head of the piston to drive the bolt carrier to the rear cycling the action. Excess gas is vented through ports in the gas tube, or in the case of the AKM and AK-74, through ports in the gas block.

One of Marc Krebs’ more unique designs is his prototype gas trap AK, a highly modified 7.62x39mm Saiga rifle. In place of the AK standard gas port design, the rifle has been reconfigured into a modern gas trap weapon. In theory, a gas trap design is more accurate. There is no gas pressure directed toward the piston until the bullet leaves the barrel, thus the piston and bolt carrier do not begin to cycle rearward until after the bullet is on its way to the target. The gas trap system is essentially an expansion chamber located at the muzzle, which diverts low pressure gas to the front of the gas piston-bolt carrier assembly driving it rearward and unlocking the action. To convert the AK to a gas trap configuration several modifications were required including an extended gas piston rod, a longer vent-less gas tube, and the fabrication of the gas trap chamber and associated parts. Marc Krebs’ gas trap AK project is an on-going development to further enhance the rifle’s accuracy; the next step Krebs is planning is to try barrels with different twist rates.

The gas trap system was originally invented in 1909 by Danish firearm designer, Soren Bang, and used in what is known as the Bang M1922 rifle. The Bang rifle was used by both Denmark and the United States. The gas trap system has been rediscovered and has gained interest in the firearms world. More recently a modified gas trap system has been adapted to the AR-15/M16 weapon system by several companies. Another company is offering reproduction gas trap parts to convert M1 Garand rifles to the system.

Some documented disadvantages to the gas trap system have been fouling and corrosion from dirty gases. The close tolerance parts required in the gas trap system make the system very hard to clean and maintain under normal operating conditions in the field. While problematic for military weapons, it would far less critical in a civilian environment.

Although the Krebs’ gas trap AK is a one of a kind prototype and unavailable to consumers, Krebs Custom offers a variety of other AK rifles to satisfy everyone from the purist to the modern tactical rifle aficionado. Offerings range from their AK-103 clone to highly modified models like the KTR-08 rifle with such features as a three-rail handguard, light single-stage trigger, enhanced safety lever, thumb-operated selector, windage adjustable aperture rear sights with a M1913 Picatinny rail, and VLTOR telescoping stocks. Krebs Custom AK rifles are available in many popular calibers to include 6.5 Grendel, 7.62x39mm, 7.62x51mm (.308) and 12 gauge semiautomatic Saiga shotguns.

For those desiring to upgrade their own AK rifles, Krebs’ line of parts and accessories are available separately. Krebs offers a number of items designed to enhance the appearance or functionality of AK pattern rifles. Some of the items available include; vertical foregrips, AK-74 pattern muzzle brakes in .22 or .30 caliber, VLTOR flashlight holders, enhanced selector levers with a bolt hold-back feature, aperture style rear sights, custom shotgun sights, Picatinny rail fore-ends and VLTOR AR-15 type telescoping buttstocks designed for AK rifles.

Note: Due to the ever-changing availability of rifles, parts, part sets and magazines, it is suggested that the company be contacted directly for current availability of their products and services.

Potential buyers should check their local and state laws, which may prohibit ownership of semiautomatic AK type rifles.

Krebs Custom
1000 Rand Rd
Wauconda, IL 60084
Ph: (847) 487-7776
Fax: (847) 487-7778
Email: krebscustom@krebscustom.com
Website: www.krebscustom.com/index.shtml

This article first appeared in SmallArmsReview.com on May 10, 2013


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